AU2012101609A4 - Valve - Google Patents

Abstract

Abstract A valve 1 has a body 2 with an inlet 4 for fluid to enter the body 2 and an outlet 6 for fluid to exit the body 2. A valve seat 44 and a piston member 8 are located in the body 2. The piston member 8 has a piston head 18 that is spaced from the valve seat 44 in an open condition of the valve 1 and seatable on the valve seat 44 in a closed condition of the valve 1. A spring 10 biases the piston member 8 in a first direction D to space the piston head 18 from the valve seat 44. A piston housing 12 is provided in the body 2 and at least part of the piston member 8 is retained in the piston housing 12. In the closed condition of the valve 2, the downstream fluid pressure, that acts to counter the spring force, acts only on the piston head 18. -4o \6 6k 1., \Vo

Description

P/00/011 28/5/91 Regulation 3.2 AUSTRALIA Patents Act 1990 ORIGINAL COMPLETE SPECIFICATION INNOVATION PATENT Name of Applicant: Australian Valve Group Pty Ltd Actual Inventor: Marcus Eric Ullrot Address for service is: GoIja Haines & Friend PO Box 1417 West Leederville Western Australia 6901 Invention Title: "Valve" The following statement is a full description of this invention, including the best method of performing it known to us: 1 Title "Valve" Field of the Invention The present invention relates to a valve. 5 Throughout this specification, unless the context requires otherwise, the word "comprise" and variations such as "comprises", "comprising" and "comprised" are to be understood to imply the presence of a stated integer or group of integers but not the exclusion of any other integer or group of integers. Throughout this specification, unless the context requires otherwise, the word 10 "include" and variations such as "includes", "including" and "included" will be understood to imply the inclusion of a stated integer or group of integers but not the exclusion of any other integer or group of integers. Background Art The discussion of the background art, any reference to a document and any 15 reference to information that is known, which is contained in this specification, is provided only for the purpose of facilitating an understanding of the background art to the present invention, and is not an acknowledgement or admission that any of that material forms part of the common general knowledge in Australia or any other country as at the priority date of the application in relation to which this specification 20 was filed. Valves are known in the art that may be used in plumbing installations to control an inlet supply line pressure to an adjustable maximum and to remain in the open condition if the pressure in the supply line falls below the maximum pressure of the valve. In addition, such valves may be used in household appliances, such as 25 dishwashers, washing machines, tap mixers and water filtering systems. They may also be used in plumbing installations to reduce water hammer. Such prior art valves are provided with a spring that biases the piston member to an open condition of the valve. They are also provided with one or more channels 2 extending from the downstream side of the valve seat to a chamber located adjacent a disc, or diaphragm, against which the spring acts to bias the piston member to an open condition of the valve. Fluid from the downstream side of the valve seat is able to flow into the chamber via the channels. In the closed condition of the valve, fluid in 5 the chamber acts against the spring force to counter the action of the spring that biases the piston member. However, such prior art valves can be somewhat bulky in size relative to the function they perform. The size translates to weight due to the corresponding amount of material needed to manufacture the valves. Their size and weight results in an 10 increase in the manufacturing costs and the end cost to a purchaser. Disclosure of the Invention In accordance with one aspect of the present invention there is provided a valve comprising a body, 15 an inlet for fluid to enter the body and an outlet for fluid to exit the body, a valve seat and a piston member located in the body, the piston member having a piston head that is spaced from the valve seat in an open condition of the valve and seatable on the valve seat in a closed condition of the valve, spring means to bias the piston member in a first direction to space the piston head 20 from the valve seat, and a piston housing provided in the body and at least part of the piston member is retained in the piston housing, wherein, in use, in the closed condition of the valve, the downstream fluid pressure that acts to counter the spring force acts only on the piston head. 25 Preferably, the piston member is provided with a cavity and the spring is at least partly located in the cavity and biases the piston member in the first direction such that a fluid flow path is formed between the inlet and the outlet in an open condition of the valve. 3 Preferably, the cavity is provided in the said at least part of the piston member that is retained in the piston housing such that at least part of the spring is surrounded by the piston housing. Preferably, a portion of the outer surface of the piston housing is substantially 5 adjacent an inside surface of the body. Preferably, at least one seal is provided between the outer surface of the piston housing and the inside surface of the body. Preferably, the valve further comprises adjuster means to adjust the spring force with which the spring means biases the piston member in the first direction. 10 Preferably, at least the piston member and the piston housing may be inserted into and removed from the body as a unit. Preferably, the valve further comprises strainer means, in use, to filter fluid entering the body via the inlet. In one embodiment, the valve head is provided with a seal which is compressed 15 mainly radially by the valve seat in the closed condition of the valve. In one embodiment, the valve seat is fixed to the body, for example, by a press-fit connection. In another embodiment, the valve seat is connected with the piston housing. This enables the piston member, the piston housing and the valve seat to be inserted into 20 and removed from the body as a unit. Brief Description of the Drawings The present invention will now be described, by way of example only, with reference to the accompanying drawings, in which: Figure 1A is a perspective view of a first embodiment of a valve in accordance with 25 the present invention; Figure 1B is a first cross-sectional view of the valve, shown in Figure 1A, in an open condition; Figure 1C is a second cross-sectional view of the valve, shown in Figure 1A, in a closed condition; 4 Figure 1D is a perspective view of the piston member, without the piston screw, 0 ring piston seal and O-rings, of the valve shown in Figure 1A; Figure 1 E is a side view of the piston member shown in Figure 1D; Figure 1 F is a longitudinal cross-sectional view of the piston member shown in Figure 5 1D; Figure 1G is a perspective view of the valve seat of the valve shown in Figure 1A; Figure 1H is a cross-sectional view of the valve seat shown in Figure 1G; Figure 11 is a perspective view of the piston housing; Figure 1J is a cross-sectional view of the piston housing shown in Figure 1I; 10 Figure 1K is a second cross-sectional view of the valve, shown in Figure 1A, in an open condition, in which surfaces of the piston member have been labelled; Figure 1L is a schematic illustration of the projected areas on the YZ plane of the pressure acting on the surfaces, of the piston member, as illustrated in Figure 1K; Figure 2A is a first cross-sectional view of a second embodiment of a valve in 15 accordance with the present invention, in an open condition; Figure 2B is a second cross-sectional view of the valve, shown in Figure 2A, in a closed condition; Figure 2C is a perspective view of the piston member, without the piston nut, piston seal and O-rings, of the valve shown in Figure 2A; 20 Figure 2D is a side view of the piston member shown in Figure 2C; Figure 2E is a longitudinal cross-sectional view of the piston member shown in Figure 2C; Figure 2F is a perspective view of the piston housing and valve seat without the 0 rings, of the valve shown in Figure 2A; 25 Figure 2G is a side view of the piston housing and valve seat shown in Figure 2F; Figure 2H is a longitudinal cross-sectional view of the piston housing and valve seat shown in Figure 2F; 5 Figure 3A is a perspective view of a third embodiment of a valve in accordance with the present invention; Figure 3B is a side view of the valve shown in Figure 3A; and, Figure 3C is a cross-sectional view of the valve, shown in Figure 3A, in a closed 5 condition. Best Mode(s) for Carrying Out the Invention In Figures 1A to 1L, there is shown a valve 1 in accordance with a first embodiment of the present invention. The valve 1 comprises a body 2, an inlet 4 for fluid to enter the body 2, an outlet 6 for 10 fluid to exit the body 2, a piston member 8 moveable within the body 2, a spring 10 to bias the piston member 8 in a first direction, shown by the arrow D in Figures 1B and 1C, and a piston housing 12 provided in the body 2. At least part of the piston member 8 is retained in the piston housing 12. The body 2 comprises a main (body) portion 14 and an offset (body) portion 16, 15 (provided with a nut), which extends from the main portion 14 is a substantially transverse arrangement. The offset portion 16 is provided with the inlet 4 and the main portion 14 is provided with the outlet 6. With particular reference to Figures 1B to 1F, the piston member 8 comprises a piston head 18, a base 20 and a neck 22, which extends between the piston head 18 20 and the base 20. A cavity 24 is provided in the base 20 of the piston member 8. The base 20 has an opening 26. The spring 10 is at least partly located in the cavity 24. A portion of the spring 8 extends from the cavity 24 via the opening 26. If the cavity 24 was not provided, the valve would not be as compact since the spring 10 would bear against the end of the base 20 of the piston member 18. 25 A shoulder 28 is provided at the piston head 18, along with a seal in the form of an 0 ring 30 that abuts the shoulder 28, and a screw 32 that retains the 0-ring 30 in place between the shoulder 28 and the screw 32. The screw 32 engages with a screw thread 34 at the end of the piston member 8 at which the piston head 18 is provided. The piston head 18 is shaped substantially to resemble an oblate spheroid, with the 30 0-ring 30 provided at the circumference of its mid region, which in the case of an oblate spheroid, may be referred to as the equatorial circumference. 6 The piston member 8 is provided with a shoulder 36. The shoulder 36 is formed at the region between the base 20 and the neck 22. The neck 22 has a curved surface 38. As best seen when the piston member 8 is viewed to see its longitudinal dimension, the curved surface 38 has a gradually decreasing cross-sectional 5 diameter from the respective ends of the neck 22 to the mid region of the neck 22, i.e. from the respective ends of the neck 22 adjacent the shoulder 36 and the piston head 18, toward the mid region of the neck 22. As best seen in Figures 1D to 1F, the base 20 of the piston member 8 is provided with circumferential grooves 40. The grooves 40 accommodate respective O-rings 10 42, as best seen in Figures 1B and 1C. Figures 1D to 1 F show the piston member 8, without the O-ring 30, screw 32 and the O-rings 42. The piston member 8 is moveable in the body 2 between an open condition and a closed condition of the valve 1, as will be later described herein. A valve seat 44 is provided in the body 2. The valve seat 44 can be seen in Figures 15 1B and 1C and is shown separately in Figures 1G and 1H. The valve seat 44 defines an upstream side and a downstream side. The upstream side of the valve seat 44 is the side that is in fluid communication with the inlet 4 and the downstream side is the side that is in fluid communication with the outlet 6. The valve seat 44 is substantially annular in shape. The valve seat 44 has a seating surface 46 around an opening 48 20 through the valve seat 44. The seating surface 46 has a chamfered portion 47, adjacent the downstream side of the valve seat 44, and an adjoining portion 49 at the inner mid region of the valve seat 44. The valve seat 44 is provided with a groove 50 in its outer surface. An O-ring 52 is located in the groove 50. The valve seat 44 is retained in position by a press-fit of the valve seat 44 into the body 2. The O-ring 52 25 seals against the internal surface of the body 2 to ensure that fluid cannot leak between the wall of the body 2 and the valve seat 44. The valve 1 may also comprise an adjuster 54 to adjust the spring force with which the spring 10 biases the piston member 8 in the first direction D. This, in turn, adjusts the maximum pressure of the valve 1, as will be further described herein. 30 The base 20 of the piston member 8 is retained in the piston housing 12. The piston housing 12 is substantially in the form of a sleeve. At least a portion of the outer surface of the piston housing 12 is substantially adjacent, i.e. contiguous, with the inside surface of the body 2. The piston housing 12 is provided with a groove 56 to accommodate an O-ring 58 on the outer side of the housing 12. A shoulder 60 is 7 provided on the outer side of the piston housing 12. The piston housing 12 is provided with an inwardly turned flange 61 at one end thereof. The O-ring 58 forms a seal between the outer surface of the piston housing 12 and the inside surface of the body 2 to prevent fluid leaking from the valve 1. The O-rings 5 42 form seals between the inside surface of the piston housing 12 and the outer surface of the base 20 of the piston member 8 to prevent fluid leaking into the cavity 24 and coming into contact with the spring 10. The cross-sectional diameter of the neck 22 of the piston member 8 is less than the diameter of the opening 48 of the valve seat 44. This allows the neck 22 to pass 10 freely, in either direction (i.e. in the direction D or the direction opposed to the direction D), through the opening 48 when the piston member 8 moves within the body 2. The adjuster 54 comprises a nut 62 and a screw 64 located in a cap 66. The screw 64 screw-threadedly engages with the nut 62. The screw 64 can be turned from 15 outside the cap 66 to move the nut 62 along the shaft of the screw 64 in the cap 66. The screw 64 may be turned in the appropriate direction to adjust the spring force with which the spring 10 biases the piston member 8 in the direction D, i.e. to adjust the force with which the spring 10 biases the piston member 8 to unseat the piston head 18 from the valve seat 44. Depending upon the direction in which the screw 64 20 is turned, the nut 62 moves along the shaft of the screw 64 toward or away from the piston member 8 to thereby, respectively, increase or decrease the spring force. Adjusting the spring force of the spring 10 in this way adjusts the maximum pressure of the valve 1. Thus, increasing the spring force increases the maximum pressure and decreasing the spring force decreases the maximum pressure. 25 The cap 66 is connected to the body 2. The connection may be a screw-threaded connection 67 between the cap 66 and the body 2. The piston housing 12 is retained in position in the body 2 by the cap 66. In that regard, the shoulder 60 of the piston housing 12 sits on an annular ledge in the inside wall of the body 2. The cap 66 abuts against an end of the piston housing 12. When 30 the cap 66 is connected to the body and tightened, it secures the piston member 12 in place in the body 2. An end of the spring 10 abuts with the nut 62. The spring 10 is retained between the nut 62 and an abutment surface, or edge, 68 of the base 20 inside the cavity 24. 8 Since the spring 10 is at least partly located in the cavity 24, in the base 20 of the piston member 8, and the base 20 is retained in the piston housing 12, the piston housing surrounds that portion of the spring 10. That is to say, the base 20 is located between the piston housing 12 and that portion of the spring. 5 The valve 1 is provided with a stop 69 for the piston member 8. The stop 69 limits the travel of the piston member 8 in the direction opposed to the direction D. The stop 69 may be provided in the cap 66. The body 2 is provided with suitable connection means to connect the valve 1 to pipes such as, for example, pipes in a plumbing installation. In that regard, a screw 10 thread 70 is provided at the inlet 4 and a screw thread 72 is provided at the outlet 6. The screw threads 70 and 72 are used, in use, to connect the valve 1 to the pipes, such as pipes in a plumbing installation. Figures 1B and 1C show the screw thread 70 as being on the interior of the body 2 (i.e. a female screw thread) and the screw thread 72 as being on the exterior of the body 2 (i.e. a male screw thread). However, 15 any type of screw thread may be used such that the valve 1 may be connected in a plumbing installation as required. The piston member 8 and the piston housing 12 may be inserted into and removed from the body 2 as a unit, i.e. the piston member 8 and the piston housing 12 form a cartridge. Removal may be performed by disconnecting the cap 66 from the body 2 20 via the screw-threaded connection 67 and then removing the piston member 8 and the piston housing 12 along with the spring 10. Some resistance may be encountered when the O-ring 30 passes through the opening 48 of the valve seat 44, but this does not prevent removal. The steps for insertion are opposite to those fro removal. The valve 1 is provided with a strainer 74. The strainer 74 filters fluid entering the 25 body via the inlet 4. The strainer 74 prevents particulate debris, which may be entrained in the fluid, from passing into the main portion 14 of the body 2 of the valve 1 and interfering with the piston member 8, valve seat or internals of the main portion 14 of the body 1. The strainer 74 may be provided as a cylindrical mesh in the main portion 14 opposite the offset portion 16. 30 The spring 10 biases the piston member 8 in the direction D, i.e. to bias the valve head 18 away from the valve seat 44 to an unseated condition, such that a fluid flow path is formed between the inlet 4 and the outlet 6 in an open condition of the valve 1, as will be further described herein. 9 The spring 10 biases the piston member 8 in the direction D to an open condition of the valve 1, i.e. to move the piston head 18 away from the valve seat 44. In an open condition of the valve 1, the piston head 18 is unseated from the valve seat 44 and the O-ring 30 of the piston head 18 is not in contact with the seating surface 46 of the 5 valve seat 44. In an open condition of the valve 1, a fluid flow path is formed between the inlet 4 and the outlet 6, the fluid flow path extending from the inlet 4 to the outlet 6, as will be further described herein. The fully open condition of the valve 1 occurs when the piston member 8 has moved within the body 2, in the direction D, such that the shoulder 36 of the piston member 8 abuts against the flange 61 of the piston 10 housing 54. Once the shoulder 36 abuts against the flange 61, further movement of the piston member 8 in the direction D is not possible. The maximum possible spacing between the piston head 18 and the seating surface 46 of the valve seat 44 occurs when the shoulder 36 abuts against the flange 61, i.e. when the valve 1 is in the fully open condition. The fully open condition of the valve 1 is shown in Figure 1B. 15 The shapes of the piston head 18, the valve seat 44 and the curved surface 38 of the neck 22 result in the fluid flow path at the region near the opening 48, of the valve seat 44, having a substantially constant cross-sectional area that results in a relatively smooth flow of fluid through the opening 48 and around the piston head 18. In the closed condition of the valve 1, the piston head 18 seats on valve seat 44 such 20 that the O-ring 30 is in sealing contact with the seating surface 46 of the valve seat 44. In the closed condition of the valve 1, the O-ring 30 normally wedges against and seat on the chamfered portion 47 of the seating surface 46 at the region adjacent the adjoining surface 49. However, it may seat on the adjoining surface 49 under some conditions such as, for example, in the event of a shock pressure rise on the 25 downstream side of the valve seat 44. The closed condition of the valve 1 is shown in Figure 1C. In the closed condition of the valve 1, the fluid cannot pass through the opening 48 of the valve seat 44. Accordingly, in the closed condition of the valve 1, there is no flow path that extends between the inlet 4 and the outlet 6 since the opening 48 of the valve seat 44 is closed off by the piston head 18. 30 In the closed condition of the valve 1, fluid on the upstream side of the valve seat 44 is separated from fluid on the downstream side of the valve seat 44. The manner of use and operation of the valve 1 of the present invention will now be described. 10 In use, the valve 1 may be installed in a fluid supply line such as, for example, the supply line to a hot water heater, to limit the inlet supply line pressure to a maximum pressure to which the valve 1 has been set via the adjuster 54. The valve 1 is connected into the fluid supply line by way of the screw threads 70 and 72. Fluid that 5 flows in the fluid supply line enters the valve 1 via the inlet 4 and exits via the outlet 6. The pressure of fluid, at the outlet 6, which has passed through the valve 1, cannot exceed the maximum pressure to which the valve 1 has been set via the adjuster 12. In addition, the valve 1 will remain in an open condition if the pressure of the fluid in the supply line, connected to the inlet 4 of the valve 1, falls below the maximum 10 pressure to which the valve 1 has been set. The maximum pressure of the valve 1 may be adjusted using the adjuster 12. The maximum pressure may be adjusted between a range, e.g. 150 kPa to 600 kPa. The valve 1 may be supplied from the factory at a particular maximum pressure, e.g. 500 kPa, and the maximum pressure may be subsequently adjusted, if required, at the 15 time of installation of the valve 1. The maximum pressure to which the valve 1 is adjusted, indicates the maximum pressure, as measured at the outlet 6, at which fluid is able to pass through the valve 1. In use, once flow of fluid commences through the fluid supply line (in which the valve 1 is connected), fluid flows into the valve 1 via the inlet 4. Flow of fluid through the 20 fluid supply line may be commenced, for example, by opening a fluid outlet device (such as a tap) downstream of the valve 1. A fluid flow path is formed that extends between the inlet 4 and the outlet 6 through the valve 1 as will be now described. The fluid enters the body 2 of the valve 1 via the inlet 4, passes through the offset portion 16 and into the main portion 14. The biasing action of the spring 10 on the piston 25 member 8, in the direction D, and the pressure of the fluid flowing into the valve 1, maintain the piston head 18 in an unseated condition from the valve seat 44 and the O-ring 30 is out of contact with the seating surface 46 of the valve seat 44, i.e. the valve 1 is maintained in an open condition, with the piston head 18 on the downstream side of the valve seat 44. Consequently, the fluid is able to flow from the 30 upstream side of the valve seat 44, through the opening 48 in the valve seat 44, around the piston head 18 and to the downstream side of the valve seat 44. The fluid exits the body 2 of the valve 1 via the outlet 6. In this way, a fluid flow path is formed which extends between the inlet 4 and the outlet 6 in an open condition of the valve 1. 11 In the event that the pressure of the fluid entering the valve 1 via the inlet 4 falls below the maximum pressure to which the valve 1 has been adjusted, the spring 10 still continues to bias the piston member 8 in the direction D such that the piston head 18 remains unseated from the valve seat 44. Accordingly, the valve 1 remains in an 5 open condition even if the pressure of the fluid entering the valve 1 falls below the maximum pressure to which the valve 1 has been adjusted. Figures 1K and 1L schematically illustrate the fluid pressure acting on the piston member 8 in the open condition of the valve 1. The legend for the labelling used in Figure 1K is set out below: 10 A 1 = Surface 1's (Si) projected area on the YZ-Plane

A

2 = Surface 2's (S 2 ) projected area on the YZ-Plane

A

3 = Surface 3's (S 3 ) projected area on the YZ-Plane Ares = The resulting projected area on the YZ-Plane after combining the respective projected areas (with - or + to indicate the direction of the forces produced by the 15 pressure acting on the different surfaces of the piston member 8)

P

1 = Pressure on the upstream side of the valve seat 44 (i.e. the upstream fluid pressure)

P

2 = Pressure on the downstream side of the valve seat 44 (i.e. the downstream fluid pressure) 20 The equilibrium equation for the open condition of the valve (flow rate = 0) can be expressed as follows: k -Al - P 1

-A

1 + P 1

-A

2 - P 2

-A

3 = 0 ,(flow rate = 0 => P 1 = P 2 ) 25 P 1

-(A

1 - A 2 + A 3 ) = k -Al

P

1 - (Ares) = k -Al where: k = Spring rate of the spring 10 Al = Spring deflection of the spring 10 30 and the other parameters are as defined above. Flow of fluid through the fluid supply line (in which the valve 1 is connected) may be stopped, for example, by closing the fluid outlet device. When this occurs, the back pressure of the fluid in the fluid supply line on the downstream side of the valve seat 35 44 of the valve 1 acts in the direction opposed to the direction D (i.e. in the upstream 12 direction) against the biasing action of the spring 10. The back pressure of the fluid in the fluid supply line on the downstream side of the valve seat 44 is also referred to herein as the downstream fluid pressure. This downstream fluid pressure acts on the piston head 18 to move the piston member 8 in the direction opposed to the direction 5 D until the piston head 18 seats on the valve seat 44 with the O-ring 30 in sealing contact with the seating surface 46 of the valve seat 44 to thereby close the valve 1. The stop 69 prevents the piston member 8 from moving any farther in the direction opposed to the direction D since the end of the base 20 abuts with the stop 69 in the closed condition of the valve 1. The O-ring 30 on the piston head 18 is compressed 10 mainly radially, i.e. towards its centre line, by the seating surface 46 of the valve seat 44 when the valve is in the closed condition and prevents fluid from passing through the opening 48 of the valve seat 44. (A small component of the compressive forces acting on the O-ring 30 will also act in the direction D due to the angled geometry of valve seat 44.) 15 In the closed condition of the valve, the downstream fluid pressure acts to counter the spring force of the spring 10 that acts to bias the piston member 8 to unseat the piston head 18 from the valve seat 44. In addition, in the closed condition of the valve 1, this downstream fluid pressure, that acts to counter the spring force, acts only on the piston head. The transverse cross-sectional area of the surface of the piston 20 head, on which the downstream fluid pressure acts, extends from the centre line of the piston head to the outer edge of the piston head. The valve 1 is not provided with any channels extending from the downstream side of the valve seat 44 to a chamber located adjacent a disc, or diaphragm, against which the spring 10 acts. 25 Accommodating part of the spring 10 within the cavity 24, provided in the piston member 8, results in the valve 1 having a compact size and structure. In particular, this results in the main portion 14 of the body 2 having a shorter length. Not providing any channels and chamber also results in the valve 1 having a compact size and structure. In particular, this results in the main portion 14 being narrower. 30 In Figures 2A to 2H, there is shown a valve 200 in accordance with a second embodiment of the present invention. The valve 200 has many parts that are similar to those of the valve 1 of the first embodiment. The drawings of the first and seconds embodiments of the valves 1 and 200 use the same reference numerals to denote similar parts. Those parts will not 13 again be described with reference to the valve 200 of the second embodiment. It is to be understood that the description of such parts with reference to the valve 1 of the first embodiment also applies to the valve 200 of the second embodiment. Accordingly, the description of the valve 200 will focus on the aspects of the valve 5 200 that are different from the valve 1. In that regard, the valve 200 has a piston member 8a, valve seat 44a and piston housing 12a that are different from the corresponding parts of the valve 1. In particular, the piston member 8a comprises a piston head 18a, a base 20a and a neck 22a. A cavity 24a is provided in the base 20a of the piston member 8a. The 10 base 20a has an opening 26a. The spring 8a extends from the cavity 24a via the opening 26a. A shoulder 28a is provided at the piston head 18a, along with a seal in the form of a flat seal 30a that abuts the shoulder 28a, and a nut 32a that retains the seal 30a in place between the shoulder 28a and the nut 32a. The nut 32a engages with a screw 15 thread 34a on a projection 202 at the end of the piston member 8a at which the piston head 18a is provided. The piston member 8a is provided with a shoulder 36a. The shoulder 36a is formed at the region between the base 20a and the neck 22a. The neck 22a may be longer than the neck 22 of the valve 1. The neck 22a is provided with a straight portion 204 20 in its mid region and a cone-like surface 206 at the region where the neck 22a joins the base 20a. A curved surface 208 is provided at the region where the neck 22a joins the piston head 18a. As best seen in Figures 2C to 2E, the base 20a of the piston member 8a is provided with circumferential grooves 40a. The grooves 40a accommodate respective O-rings 25 42a, as best seen in Figures 2A and 2B. Figures 2C to 2E show the piston member 8a, without the O-ring 30a, nut 32a and the O-rings 42a. The spring 10 is retained between the nut 62 and an abutment surface, or edge, 68a of the base 20a inside the cavity 24a. The piston member 8a is moveable in the body 2 between an open condition an a 30 closed condition of the valve 200. In the closed condition of the valve 200, the piston head 18a seats on the valve seat 44a with the seal 30a in sealing contact with the seating surface 46a of the valve seat 14 44a to thereby close the valve 200. The seating surface 46a is provided at the downstream end of the valve seat 44a. The seal 30a is compressed by the seating surface 46a in the direction D as well as radially towards and outwardly of its centre line. 5 The valve 200 is provided with a housing unit 210. The housing unit 210 incorporates the piston housing 12a and the valve seat 44a of the valve 200. The piston housing 12a and the valve seat 44a are connected by members 212 that extend therebetween, with spaces between the members 206 for passage of fluid. The valve seat 44a has a seating surface 46a. 10 The valve seat 44a is provided with a groove 50a in its outer surface. An O-ring 52a is located in the groove 50a. The base 20a of the piston member 8a is retained in the piston housing 12a. The piston housing 12a is substantially in the form of a sleeve. The piston housing 12a is provided with a groove 56a to accommodate an O-ring 58a on the outer side of the 15 housing 12a. A shoulder 60a is provided on the outer side of the housing 12a. The piston housing 12a is provided with an inwardly turned flange 61a at one end thereof. The piston member 8a, the piston housing 12a and the valve seat 44a may be inserted into and removed from the body 2 as a unit, i.e. the piston member 8a, the piston housing 12a and the valve seat 44a form a cartridge. Removal may be 20 performed by disconnecting the cap 66 from the body 2 via the screw-threaded connection 67 and then removing the piston member 8a, the piston housing 12a, the valve seat 44a, along with the spring 10. The steps for insertion are opposite to those fro removal. The remaining parts, features and the manner of use and operation of the valve 200 25 are the same as for the valve 1 of the first embodiment and will not be again repeated. However, it is to be understood that the description of those aspects of the valve 1 also applies to the valve 200. In Figures 3A to 3C, there is shown a valve 300 in accordance with a third embodiment of the present invention. 30 The valve 300 has many parts that are similar to those of the valve 1 of the first embodiment. The drawings of the first and third embodiments of the valves 1 and 300 use the same reference numerals to denote similar parts. Those parts will not again be described with reference to the valve 300 of the third embodiment. It is to be 15 understood that the description of such parts with reference to the valve 1 of the first embodiment also applies to the valve 300 of the third embodiment. Accordingly, the description of the valve 300 will focus on the aspects of the valve 300 that are different from the valve 1. 5 In that regard, the valve 300 has a body, or housing, 2b that is different from the body, or housing, 2 of the valve 1 of the first embodiment. In particular, the valve 300 has an in-line arrangement of the inlet 4b and the outlet 6b, whereas the valve 1 has an offset arrangement of the inlet 4 and the outlet 6. The body 2b of the valve 300 comprises a main (body) portion 302, an inlet (body) portion 10 304 and an outlet (body) portion 306. The inlet portion 304 is provided with the inlet 4b and the outlet portion 306 is provided with the outlet 6b. The inlet portion 304 and the outlet portion 306 are shown as provided with female screw threads 70. However, any suitable connection may be used to connect the valve 300 into a pipework installation. 15 The remaining parts, features and the manner of use and operation of the valve 300 are the same as for the valve 1 of the first embodiment and will not be again repeated. However, it is to be understood that the description of those aspects of the valve 1 also applies to the valve 300. Whilst preferred embodiments of the present invention have been herein before 20 described, the scope of the present invention is not limited to those specific embodiments, and may be embodied in other ways, as will be apparent to a skilled addressee. Modifications and variations such as would be apparent to a skilled addressee are deemed to be within the scope of the present invention. 25 16

Claims (13)

1. A valve comprising a body, an inlet for fluid to enter the body and an outlet for fluid to exit the body, 5 a valve seat and a piston member located in the body, the piston member having a piston head that is spaced from the valve seat in an open condition of the valve and seatable on the valve seat in a closed condition of the valve, spring means to bias the piston member in a first direction to space the piston head from the valve seat, and 10 a piston housing provided in the body and at least part of the piston member is retained in the piston housing, wherein, in use, in the closed condition of the valve, the downstream fluid pressure that acts to counter the spring force acts only on the piston head.

2. A valve according to claim 1, wherein the piston member is provided with a cavity 15 and the spring is at least partly located in the cavity and biases the piston member in the first direction such that a fluid flow path is formed between the inlet and the outlet in an open condition of the valve.

3. A valve according to claim 2, wherein the cavity is provided in the said at least part of the piston member that is retained in the piston housing such that at least 20 part of the spring is surrounded by the piston housing.

4. A valve according to any one of the preceding claims, wherein a portion of the outer surface of the piston housing is substantially adjacent an inside surface of the body.

5. A valve according to claim 4, wherein at least one seal is provided between the 25 outer surface of the piston housing and the inside surface of the body.

6. A valve according to any one of the preceding claims, further comprising adjuster means to adjust the spring force with which the spring means biases the piston member in the first direction. 17

7. A valve according to any one of the preceding claims, wherein at least the piston member and the piston housing may be inserted into and removed from the body as a unit.

8. A valve according to any one of the preceding claims, further comprising strainer 5 means, in use, to filter fluid entering the body via the inlet.

9. A valve according to any one of the preceding claims, wherein the valve head is provided with a seal, which is compressed mainly radially by the valve seat in the closed condition of the valve.

10. A valve according to any one of the preceding claims, wherein the valve seat is 10 fixed to the body.

11. A valve according to claim 10, wherein the valve seat is fixed to the body by a press-fit connection.

12. A valve according to any one of claims 1 to 11, wherein the valve seat is connected with the piston housing such that the piston member, the piston 15 housing and the valve seat are insertable into and removable from the body as a unit.

13. A valve substantially as herein before described with reference to Figures 1A to 1L; Figures 2A to 2H; or Figures 3A to 3C of the accompanying drawings. 18